1. Field of the Invention
The present invention relates to an improved cushion member for use in a vehicle seat which is formed of a foam material, such as polyurethane foam.
2. Description of the Prior Art
In most cases, a cushion member for a vehicle seat is conventionally formed of foam materials, such as polyurethane foam. Such foam materials not only exhibit excellent seat cushioning properties but are also well suited for mass production. It is also known, however, that such foam materials are still under improvement to cope with greater structural demands. That is, such foam materials are required to be capable of slightly hardening at the peripheries of the cushion member so as to eliminate deterioration of sitting comfort, while at the same time change its cushioning function in accordance with load distributions. Conventionally, in order to deal with these requirements, other separate materials are applied to the peripheral portions or desired locations of the cushion member, or alternatively a metal wire is embedded within the foam material.
These conventional means, however, cannot be said to have eliminated all drawbacks in the prior art foam cushion members. Specifically, the former means is accompanied by another disadvantage, that is, its step of applying separate members complicates the process of manufacturing such cushion member. In the latter case, another drawback arises; the foam material used is apt to run short in and from the vicinity of the embedded metal wire.
For this reason, there has been proposed another type of cushion member in the prior art which comprises a harder side element and a softer element embedded in the central portion of the side element. With this cushion member, the contact surfaces of both of the harder side and softer central elements are oriented in the same direction as that of loads to be applied. When such a cushion member is formed simply by inserting the softer central element into the harder side element is in actual use, the entire central portion thereof is softer than other portions thereof and thus only this central portion sinks in to perform a completely separate function from the harder side element. This means that a seat incorporating such cushion member therein is not able to provide a comfortable sitting feeling to its occupant.
On the other hand, in case of a cushion member which is manufactured by bonding the side and center elements together by adhesion, since their bonded surfaces are oriented in the same direction as that of loads to be applied, no effects on dispersion of the loads can be expected and thus the cushion member will be deformed or strained substantially when it is practically used. Therefore, a seat containing such cushion member cannot be a satisfactory one.